Design Of Distillation Columns Research Articles

A Heuristic for extractive agent flow rate in extractive distillation

Distillation is the most widely used separation process for liquids separation in the industry. Even when the volatilities of the mixture are not favorable, then enhanced distillation is used. Extractive distillation is the enhanced distillation most widely used that consists in introducing a large flow rate of a third compound called extractive agent with a high boiling point that it is collected at the column bottoms and recovered in another column and reused again. Some heuristics are available for distillation column design, e.g. the optimum reflux is around 1.2 to 1.35 times the minimum reflux (or 1.1-1.2 times for refrigerated systems). Unfortunately, there is not a similar heuristic to determine the optimum extractive agent flow rate. Based on a literature review of rigorous simulations of extractive distillation processes, a heuristic is proposed that indicates that the optimum extractive distillation flow rate is which provides a Distillation Sequence Efficiency at 78 % of its maximum value. The maximum value is calculated assuming infinite flow rate of extractive agent. The Distillation Sequence Efficiency is a shortcut method available for distillation columns sequencing.

Optimal selection of operating pressure for distillation columns

Optimal design of distillation columns is complex because of many entangled design variables, such as operating pressure, reflux ratio, number of stages, product specifications, etc. Amongst these parameters, operating pressure is the premise towards more economic performance related to not only capital investment but also energy cost. A common heuristic is to arbitrarily fix the pressure if inexpensive cooling water can be used at condenser. However, it cannot always guarantee an optimum column. The traditional way to obtain the optimum pressure is to perform time-consuming iterative rigorous simulations. That is, basically no handy systematical method is available to quick determine optimum column pressure. To eliminate this research gap, this study is devoted to provide an equation-oriented shortcut optimization model to determine optimum pressure avoiding manual iterative calculation. The proposal pathway can estimate column total annualized cost considering capital and energy costs simultaneously before being used to initialize rigorous design. Feasibility and accuracy of this approach are perfectly verified on Aspen Plus through five case studies — propylene–propane, benzene–toluene, cyclohexane–cyclohexanol, methanol–water, and n-pentane–n-hexane–n-heptane systems.

Distillation design and optimization of quaternary azeotropic mixtures for waste solvent recovery

The huge amount of solvents used in the semi-conductor and display industry typically result in waste of valuable solvents which often form complex azeotropic mixtures. This study explored a recovery process of a quaternary waste solvent, comprising methyl 2-hydroxybutyrate, propylene glycol monomethyl ether acetate, ethyl lactate, and ethyl-3-ethoxy propionate. In this study, a novel shortcut column method with a graphical approach was exploited for the distillation column design of complex quaternary azeotropic mixtures. As a result, the proposed shortcut method and design procedure solved the complex separation paths successfully with less computational efforts while achieving all requirements for component purity.

Design and modeling of a microscale diabatic distillation column for small capacity ammonia–water absorption systems

The concept of diabatic distillation is applied to desorption and rectification in an ammonia–water absorption system. Results of a hydrodynamic investigation of novel components for these processes are used to develop a non-equilibrium model to predict heat and mass transfer performance. A modular modeling approach is proposed whereby physical consistency of various heat and mass transfer processes is achieved while reducing model complexity. A target vapor generation rate of 3 g s−1 with an ammonia mass fraction of 0.9985 is specified. It is shown that highly compact, lightweight desorption and rectification components can be realized. Heat source temperature and mass flow rate control are used to optimize system performance, and performance predictions are made over wide range of operating conditions. These results are also used to obtain reduced-order heat and mass transfer performance measures that facilitate incorporation of system performance into system level models and dynamic models.

Reactive Distillation Column Design for Tetraethoxysilane (TEOS) Production: Economic and Environmental Aspects

Alkoxysilanes are silicon compounds containing a Si-OR bond. The applications of tetraalkoxysilanes cover a wide range depending if the Si-OR bond remains intact or is hydrolyzed. Currently, tetraethoxysilane (TEOS) is the most prominent derivative of such silicon compound family. The best known and used method of synthesis of TEOS is the esterification reaction of SiCl4, following the old Von Ebelman’s route (1846). Tetramethoxy- and tetraethoxysilane are obtained by a technology developed in the 1990’s involving the catalyzed direct synthesis of silicon metal and either methanol or ethanol. However, there is few information about novel technologies to produce TEOS, either improved current technology or proposed new approaches. In this work, the reactive distillation (RD) is suggested to produce TEOS as an intensified technology. In general, the concept of process intensification may overcome the traditional process, since it allows design technology with reduction on equipment size, improvement in energ...

Multivariable model predictive control design of reactive distillation column for Dimethyl Ether production

Dimethyl ether (DME) as an alternative clean energy has attracted a growing attention in the recent years. DME production via reactive distillation has potential for capital cost and energy requirement savings. However, combination of reaction and distillation on a single column makes reactive distillation process a very complex multivariable system with high non-linearity of process and strong interaction between process variables. This study investigates a multivariable model predictive control (MPC) based on two-point temperature control strategy for the DME reactive distillation column to maintain the purities of both product streams. The process model is estimated by a first order plus dead time model. The DME and water purity is maintained by controlling a stage temperature in rectifying and stripping section, respectively. The result shows that the model predictive controller performed faster responses compared to conventional PI controller that are showed by the smaller ISE values. In addition, the MPC controller is able to handle the loop interactions well.

Simultaneous Design and Control of Catalytic Distillation Columns Using Comprehensive Rigorous Dynamic Models

This work addressed the rigorous modeling of catalytic distillation columns by simultaneously considering relevant phenomena such as pressure drop across the column, tray capacity constraints, non-ideal behavior of both liquid and vapor, and the column’s hydrodynamics, yet to be considered in earlier modeling studies for catalytic distillation. The developed model is applied for the simultaneous optimal design and control of catalytic distillation units, taking into account economic and set-point tracking objective functions balanced though a proposed weighting parameter estimation methodology. Results for a column for the production of ethyl tert-butyl ether show the advantages of a more comprehensive model regarding design and control decisions in comparison with previous studies: design specifications were met during the entire time horizon without sacrificing economic profitability.

Integrated Process Design and Control of Cyclic Distillation Columns

Integrated process and control design approach for cyclic distillation columns is proposed. The design methodology is based on application of simple graphical design approaches, known from simpler conventional distillation columns. Here, a driving force approach and McCabe-Thiele type analysis is combined. It is demonstrated, through closed-loop and open-loop analysis, that operating the column at the largest available driving force results in an optimal design in terms of controllability and operability. The performance of a cyclic distillation column designed to operate at the maximum driving force is compared to alternative sub-optimal designs. The results suggest that operation at the largest driving force is less sensitive to disturbances in the feed and inherently has the ability to efficiently reject disturbances.

Design of membrane cascades according to the method of McCabe-Thiele: An organic solvent nanofiltration case study for olefin hydroformylation in toluene

Abstract The method of McCabe-Thiele is widely used for the design of distillation columns. At a given pressure, this graphical method is only based on 3 equations: (i) the partitioning curve linking the liquid and gas phases for a given component at a given plate thanks to a unique set of thermodynamic data and (ii) two operating lines, each one describing the liquid/gas equilibrium of two consecutive plates either in the enrichment section or in the stripping one. In this paper, the method has been adapted to the membrane separation processes aiming at the easy selection of a first set of appropriate designs of cascades that fulfill given separation targets, especially in the case of a binary mixture of components having both intermediate rejections and very different concentrations. Membrane cascades involving several recyclings of the permeate and retentate streams are proposed according to a similar but more sophisticated methodology than for distillation, since for a selected membrane and for given hydrodynamic conditions (pressure, velocity, temperature), several proposals can be made for each equation mentioned above. In short, a set of operating lines is generated varying with the volume reduction ratio (VRR) either for the permeate or the retentate retreatment sections. The method is applied to the OSN separation of a final synthesis medium of a homogeneous catalyzed reaction, namely olefin hydroformylation achieved in toluene. This example is a typical one dealing with the more general case of a product to be extracted in the permeate and a catalytic system to be recovered in the retentate for further recycling in the synthesis reactor aiming at a greener production process. The initial concentration ratio of the two components to separate in OSN is 1/1000 and both compounds have intermediate rejections of 30% and 88%. Thanks to this method, the design of several membrane cascades is proposed and discussed according to different goals of separation (target product purity or recovery, enrichment of component to be recycled, energy consumption, etc.).

Systematic design of energy efficient distillation column for alcohol mixture

When designing a separation system for mixtures containing close boiling point components, ordinary distillation can be considered not feasible since high purity products require large number of stages and reflux ratio. During the design phase of distillation processes, several problems may occur such as determination of optimal number of plates, optimal location for feed, and optimal reflux ratio. The main objective of this paper is to propose a methodology to design an energy efficient alcohol distillation process using driving force approach. The design concept is to design the distillation column system at maximum driving force. At maximum driving force, the energy required for the system will be minimum. A case study of 5 component alcohol mixture from a literature was selected and investigated. Initially, the literature case study was analysed and simulated by using Aspen HYSYS V9’s shortcut design method to determine the energy usage and capital cost. Then, similar feed information from the shortcut design was used for a new design which was developed according to the driving force approach in the methodology. Optimum design variables were determined from the methodology. Both designs were simulated using similar thermodynamic model (RK-Aspen) to ensure reliable data for comparison purposes. Finally, both designs were analysed and compared in terms of capital and operating cost. Based on the findings, the capital cost was reduced up to 12.25 % and operation cost up to 9.39 %. The performance confirms that by using this methodology, optimum or near optimum design for alcohol distillation process can be developed in an easy, practical, and systematic manner.

Systematic design of energy efficient extractive distillation column for azeotrope mixture

The last dozen years produced so many articles on the synthesis of separation systems. For distillation systems, they can be divided into several types such as ordinary distillation and azeotropic distillation. When designing a separation system for mixtures containing azeotrope(s), ordinary distillation can be considered as not feasible since high purity products cannot be obtained. When designing a distillation based separation process, several problems may occur such as determination of optimal number of plates, optimal location for feed, and optimal reflux ratio. The main objective of this paper is to propose a methodology to design an energy efficient extractive distillation process using driving force approach. The design concept is to design the distillation column system at maximum driving force. At maximum driving force, the energy required for the system will be minimum. A case study of ethanol-water mixture from a literature was selected and investigated. Initially, the literature case study was analysed and simulated by using Aspen PLUS V9 to determine the energy usage and capital cost of the existing design. Then, the feed information from the existing design was used for a new design which was developed according to the driving force approach in the methodology. Optimum design variables were determined from the methodology. Since the literature case study used NRTL thermodynamic properties, similar package was used to ensure reliable data. Finally, both designs were analysed and compared in terms of capital and operating cost. Based on the findings, the capital cost was reduced up to 0.47 % and operation cost up to 7.61 %. Performance confirms that by using this methodology, optimum or near optimum design for extractive distillation can be developed in an easy, practical and systematic manner.

Olefin Mixture Direct Sequence Retrofitting and Feed Compositions Sensitivity Analysis

The objective of this paper is to retrofit the energy of the Olefin Mixture (OM) direct sequence and analyze the energy sensitivity with respect to the feed compositions. In order to perform the retrofitting study and energy sensitivity analysis, a methodology for retrofitting the direct sequence and analyzing the energy sensitivity with respect to the feed compositions has been developed, consists of four stages. In Stage 1, a short-cut distillation column design method of process simulator (Aspen HYSYS) is used to simulate the direct sequence. Then, the energy used to separate individual component in the direct sequence is analyzed and taken as a reference. In Stage 2, an optimal OM sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. Once the optimal OM sequence has been determined, the new optimal sequence is then simulated in Stage 3 using short-cut distillation column design method (using Aspen HYSYS), where the energy used in the optimal OM sequence is analyzed. Finally, the energy used in the optimal OM sequence is compared with the direct, direct-indirect and random sequence in Stage 4. The gains of each sequence are then calculated using the energy as the basis for the sensitivity analysis when the feed compositions are changed. From the results obtained, it can be concluded that it is possible to retrofit the direct sequence using the driving force method for better improvement in terms of energy consumptions and energy sensitivity.

Olefin Mixture Direct Sequence Energy Retrofitting: Feed Compositions Sensitivity Analysis

The objective of this research is to retrofit the Olefin Mixture (OM) direct sequence and to analyze the sensitivity with respect to the feed composition. In order to perform the study and analysis, a methodology for retrofitting the direct sequence and analyzing the sensitivity with respect to the feed composition was developed. In Stage 1, a short-cut distillation column design method of process simulator (Aspen HYSYS) is used to simulate the direct sequence. The energy used to separate individual component in the base sequence is analyzed and taken as a reference. In Stage 2, an optimal OM sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. Once the optimal OM sequence has been determined, the new optimal sequence is then simulated in stage 3 using short-cut distillation column design method (using Aspen HYSYS), where the energy used in the optimal OM sequence is analyzed. Finally, the energy used in the optimal OM sequence is compared with the direct, direct-indirect and random sequence in Stage 4. The gains of each sequence are then calculated using the energy as the basis for the sensitivity analysis. From the results obtained, it can be concluded that it is possible to retrofit the direct sequence using the driving force method for better improvement in terms of energy consumptions and sensitivity.

Heterogeneous azeotropic distillation for the separation of n-propanol + water mixture using n-propyl acetate as entrainer

Heterogeneous azeotropic distillation is a widely used process in the chemical process industries for the separation of binary azeotropic mixtures into their constituent pure components. It involves the addition of an entrainer which is partially miscible and forms a heterogeneous azeotrope preferably with one of the original components. For the design of heterogeneous azeotropic distillation columns, a detailed study of the heterogeneous region is crucial and this requires experimental vapor-liquid-liquid equilibrium (VLLE) data. The present study focuses on the study of n-propyl acetate as entrainer to effect the separation of industrially available azeotropic mixture n-propanol-water. A new and simple still was constructed to measure the VLLE data for the ternary system. The isobaric VLE data for the two binary systems n-propanol - water and n-propanol - n-propyl acetate and isobaric VLLE data for the ternary system n-propanol - water - n-propyl acetate were measured at atmospheric pressure. The experimental results have been compared with various thermodynamic models such as NRTL, UNIQUAC, UNIFAC (VLE) and UNIFAC (LLE). The set of parameters obtained from the above models has been used to construct the residue curve map (RCM) for the ternary system and the effect of n-propyl acetate to accomplish the separation of the azeotropic mixture has been discussed.

Removing krypton from xenon by cryogenic distillation to the ppq level

The XENON1T experiment aims for the direct detection of dark matter in a detector filled with 3.3 tons of liquid xenon. In order to achieve the desired sensitivity, the background induced by radioactive decays inside the detector has to be sufficiently low. One major contributor is the beta -emitter ^{85}Kr which is present in the xenon. For XENON1T a concentration of natural krypton in xenon mathrm {^{nat}mathrm{Kr/Xe},<,200,ppq} (parts per quadrillion, 1~mathrm{ppq}~=10^{-15} mathrm{mol/mol}) is required. In this work, the design, construction and test of a novel cryogenic distillation column using the common McCabe–Thiele approach is described. The system demonstrated a krypton reduction factor of 6.4cdot 10^5 with thermodynamic stability at process speeds above 3 kg/h. The resulting concentration of mathrm {^{nat}mathrm{Kr/Xe}<26,ppq} is the lowest ever achieved, almost one order of magnitude below the requirements for XENON1T and even sufficient for future dark matter experiments using liquid xenon, such as XENONnT and DARWIN.

The production zone method: A non-ideal shortcut method for the design of distillation columns

Abstract Graphical shortcut methods are useful tools for the design of distillation columns. The proposed nonideal shortcut method includes a graphical representation and is based on the concept of operation leaves. This new method uses a production segment rather than a completely specified product, which eliminates any sensitivity to the composition of the minor product. Concerning phase equilibria, no restrictive assumptions are made. The study aimed (1) to determine whether a specified separation respects the mass balance and thermodynamic feasibility and (2) to find the minimum reflux ratio for a preliminary design of the column. Designs obtained with this new method for ideal, non-ideal, and azeotropic mixtures give purity and recovery rates close to the specifications, which might be impossible to obtain with a conventional ideal shortcut like the well-known Fenske–Underwood–Gilliland shortcut method. The distillation boundaries of azeotropic mixtures are taken into account thanks to a non-ideal thermodynamic model applied to the calculation, which is not the case with a conventional ideal shortcut. The paper examines the following mixtures: an ideal mixture of ethanol, n -propanol, and n -butanol; a non-ideal mixture of acetone, water, and acetic acid; and an azeotropic mixture of acetone, isopropanol, and water.

Thermodynamic optimization of atmospheric distillation unit

This paper presents a methodology for optimising the exergy efficiency of atmospheric distillation unit without trading off the products qualities and process throughput. The presented method incorporates the second law of thermodynamics in data driven models. Bootstrap aggregated neural networks (BANN) are used for enhanced model accuracy and reliability. The standard error of the individual neural network predictions is taken as the indication of model prediction reliability and is incorporated in the optimization objective function. The economic analysis of the recoverable energy (sum of internal and external exergy losses) reveals the energy saving potential of the proposed method, which will aid the design and operation of energy efficient atmospheric distillation columns.

Optimal retrofit of natural gas liquids separation direct sequence and feed condition sensitivity analysis

The objective of this paper is to present the retrofitting analysis for the direct sequence natural gas liquids (NGLs) separation process and to analyse the process sensitivity with respect to feed conditions. To perform the study and analysis, the energy efficient NGLs separation process methodology is developed. Hence, the methodology consists of four hierarchical steps. In Step 1, a simple and reliable short-cut method for distillation column design of process simulator (Aspen HYSYS) is used to simulate a base (direct) NGLs sequence. The energy used to perform the separation is obtained that will be used for comparison purpose. In the Step 2, an optimal NGLs sequence is determined using driving force method. All individual driving force curves for all adjacent components are plotted and the optimal sequence is determined based on the plotted driving force curves. The optimal sequence is then simulated in Step 3 using a simple and reliable short-cut method (using Aspen HYSYS), where the energy used in the optimal NGLs sequence is analysed. Finally, the energy and sensitivity used in the optimal NGLs sequence is compared with the base sequence in Step 4. Several case studies involving several sequences have been used to test the performance of the developed methodology. A maximum energy saving of 11.7 MW was achieved when compared with the optimal (driving force) sequence with the direct sequence. For sensitivity analysis, the results show that the driving force sequence has the best sensitivity compared to other sequences. These findings show that the developed methodology is not only able to design energy efficient distillation columns sequence but also better process sensitivity with respect to the feed conditions for NGLs separation process in an easy, practical and systematic manner.

An Improved Restarted Adomian-based Solution for the Minimum Reflux Ratio of Multicomponent Distillation Columns

An improved version of powerful Adomian decomposition method (ADM), namely Restarted Adomian decomposition method (RADM), has been employed to find the roots of Underwood’s equations. Underwood’s equations frequently appear in the design of multi-component distillation columns and are used to get a quick estimate of minimum reflux ratio. However, due to highly nonlinear nature and presence of singularities, these equations pose convergence-related difficulties. In this communication, it is shown that RADM is not only capable of overcoming these difficulties but also the values of residual errors show that the RADM-based solutions are superior to the recently developed ADM-based solutions as well as to those obtained by using the well-known Newton–Raphson method. Besides, unlike ADM, the proposed RADM does not require convergence accelerators such as Shanks transformation and only few terms are needed to get the accurate results.

Techno Economic Optimization of Petlyuk Distillation Column Design Using Duelist Algorithm

Distillation process consume huge energy hence one of the method for reducing it is by applying Petlyuk configuration. In design stage, the important thing is the minimum number of trays. In this paper, four methods of Petlyuk configuration design were compared i.e. the short-cut method, the modified method using Winn equation, Vapor-Liquid Equilibrium (VLE) approach and the proposed method that incoorporated Duelist Algorithm Optimization (DAO) method and VLE approach. Optimization was performed by techno economic consideration. The objective is minimizing the total annual cost for operating period over 10 years. The maximum saving about 34,38% was provide when the actual number of trays at prefractionator and at main column are 3 and 109, respectively, and it's related operating condition.